Dynamoelectric machines, such as electric motors and generators, include stator cores which generally are formed of a plurality of steel laminations bonded together to form a hollow cylinder having a pair of end faces spaced apart a longitudinal distance referred to as the stack height. A plurality of teeth extend from an inner cylindrical surface of the core into a hollow center portion. The teeth form slots between adjacent teeth that extend the length or the height of the core.
Electrical conductors are disposed in the slots to react to or to generate electromagnetic fields. Generally, the conductors are coils of wire wrapped around the teeth and through the slots in a winding pattern. In an electric motor, for example, energizing the coils generates an electromagnetic field in the core to rotate a rotatable assembly in the center portion of the core. To generate the electromagnetic field and to prevent shorting, the core is electrically insulated from the coils of wire. One desirable approach is the employment of slot cell insulators fabricated from suitable insulating or dielectric material.
One type of slot cell insulator is formed by folding opposite ends of a piece of relatively thin dielectric material upon itself along parallel fold lines extending across a width of the material to form two end portions of at least double thickness dielectric material. This piece of material is then folded lengthwise along a longitudinal fold line extending approximately through the center of the material with the folded end portions on the outside. In use, a center portion of the insulator lines the walls of the slots in the stator core and prevents contact between the conductors and the stator core. The folded-over end portions form cuffs which engage respective opposite end faces of the stator core when the insulator is placed in the slot. The cuffs help the insulators remain within the slots in the stator core.
One method of inserting slot cell insulators into a stator core includes a device having a crank and slider mechanism for driving a push rod. The push rod engages a cuffed end of an insulator and longitudinally pushes the insulator past an end face and into a slot in the stator core. This method requires incrementally, rotatably indexing the stator core to position each slot to receive an insulator. Indexing the stator core to the precise position accurately and consistently is difficult, however. If the stator core is not positioned precisely, the insulator may catch on the end face adjacent the slot as the insulator is inserted.
Not only is this a slow process, but the device is difficult to adjust for different lengths of insulators used in stator cores having a different stack height. Often an entirely new device must be substituted. Furthermore, in this type of device the insulators cannot be formed until a stator core can receive them, thus the device is idle between stator cores.
In addition, the slider-crank mechanism requires an extensive amount of maintenance to ensure precise positioning of the insulator in the slot. Inserting one insulator at a time also means that incrementally rotating the stator core through three hundred and sixty degrees holds the stator core at a slot cell insulator inserting station on an assembly line for a long time.
Another problem with the prior insulator insertion devices is that sometimes on one side of the longitudinal fold in the insulator there is more material than on the other side of the longitudinal fold and thus the longitudinal side edges do not line up evenly. As a result, when the insulator is placed into a slot in the stator core, a portion of the tooth or other part of the stator core is exposed and the chances for a short circuit increase.